The present invention relates to a method for controlling movement of a first vehicle component relative to a second vehicle component. The invention is especially applicable for a work vehicle.
The term work vehicle comprises different types of material or earth handling vehicles like construction machines, such as a wheel loader, a backhoe loader and an excavator. The invention will be described below in a case in which it is applied in a wheel loader. This is to be regarded only as an example of a preferred application.
Work vehicles are for example utilized for construction and excavation work. A wheel loader may be used to transport heavy loads from one location to another, often encountering a series of turns and varying grade slopes on the route between two or more locations.
The method may be used for controlling movement of a work implement capable of being moved through a number of positions during a work cycle. Such implements typically include buckets, forks, and other material handling apparatus. The typical work cycle associated with a bucket includes sequentially positioning the bucket and associated lift arm in a digging position for filling the bucket with material, a carrying position, a raised position, and a dumping position for removing material from the bucket.
Control levers are mounted at an operator's station and are connected to an electrohydraulic circuit for moving the bucket and/or lift arms. The operator manually move the control levers to open and close hydraulic valves that direct pressurized fluid to hydraulic cylinders which in turn cause the work implement to move. For example, when the lift arms are to be raised, the operator moves the control lever associated with the lift arm hydraulic circuit to a position at which a hydraulic valve causes pressurized fluid to flow to the head end of a lift cylinder, thus causing the lift arms to rise. When the control lever returns to a neutral position, the hydraulic valve closes and pressurized fluid no longer flows to the lift cylinder.
In normal operation, the work implement is often abruptly started or brought to an abrupt stop after performing a desired work cycle function, which results in rapid changes in velocity and acceleration of the bucket and/or lift arm, vehicle, and operator. This can occur, for example, when the implement is moved to the end of its desired range of motion and can produce operator discomfort as a result of the rapid changes in velocity and acceleration.
U.S. Pat. No. 6,047,228 discloses a method for limiting the control of an implement of a work machine. A controller receives an implement position signal from an implement position sensor and an operator command signal from an operator joystick sensor. The controller comprises a plurality of look-up tables, which correspond to the work functions used to control the implement. The lookup tables are used to determine a magnitude of an electrical valve signal to a valve, which controls the implement via hydraulic cylinders. The magnitude of the electrical valve signal is determined by comparing a predetermined maximum limit value from a look-up table with the magnitude of the operator command signal and selecting the lesser value. This results in a reduction in the maximum velocity (of the work implement movement) that the operator may command. The limiting values are for example chosen to stop a pivotal movement of the implement prior to the implement reaching the physical maximum dump angle. This results in that the dampening always starts at the same point and the valve follows a predefined line to a fixed value regardless of the current implement load and relative velocity. This leads to variations in the deceleration and the forces on the cab will vary arbitrarily.
It is desirable to achieve a control method which increases operator comfort during operation of the vehicle. An aspect of the invention is especially directed to a control method that creates conditions for achieving a determined accepted force on a second vehicle component during acceleration/deceleration of a first vehicle component. Specifically, the second vehicle component comprises a vehicle frame and the first vehicle component comprises a work implement.
A method according to an aspect of the present invention comprises the steps of determining a deceleration rate of the first vehicle component in order to achieve a predetermined final speed at a final position, determining a starting position for initiating the deceleration on the basis of the predetermined final speed, the final position and the determined deceleration rate and controlling deceleration of the first vehicle component from the starting position to the final position according to the determined deceleration rate.
According to one embodiment of the invention, the method is applied for end dampening of a work implement. Thus, the final position may represent a geometrical or a mechanical end position or be in the vicinity of the end position and the final speed at the final position is zero or close to zero.
According to a further embodiment of the invention, the method comprises the step of detecting a vehicle operation parameter before initiating the deceleration and determining the starting position also on the basis of the detected vehicle operation parameter. Especially, a speed of the first vehicle component relative to the second vehicle component is detected. Preferably, the detected operation parameter is indicative of an angular speed of the first vehicle component. Thus, the starting point for initiating the controlled deceleration varies for different detected operative conditions. This creates further conditions for achieving a predetermined force on the second vehicle component regardless of the magnitude of the detected vehicle operation parameter.
According to a further embodiment of the invention, the method comprises the step of detecting a vehicle operation parameter and calculating a deceleration rate as a function of the detected vehicle operation parameter. Especially, a load is detected. Preferably, a pressure in a vehicle hydraulic system is detected, wherein the hydraulic system is adapted to move the first vehicle component relative to the second vehicle component and the detected hydraulic pressure represents the load.
Thus, the starting point for initiating the controlled deceleration is based on both the angular speed of the first vehicle component and the load.
According to a further development of the last mentioned embodiment, the deceleration rate has an inverse relationship to the detected load. The force (F) subjected to the second vehicle component equals the load, or weight, (m) multiplied by the acceleration (or deceleration) (a). By using the inverse relationship, the deceleration may be controlled so that the second vehicle component is subjected to the same force regardless of the magnitude of the detected load.
According to an alternative to the last mentioned embodiment, the method comprises the step of using a predetermined deceleration rate. Thus, this predetermined deceleration rate may be independent from the load. In other words, the magnitude of the load is estimated, and the starting position will be dependent on the initial first vehicle component relative speed.
It is also desirable to achieve a determined accepted force on a second vehicle component during positive acceleration of a first vehicle component, such as a work implement, i.e. during a motion starting procedure. The term “positive acceleration” has the meaning of a speed increase. The second vehicle component may be formed by a vehicle frame.
A method according to an aspect of the present invention comprises the steps of determining an acceleration rate in order to achieve an increased, predetermined final speed at a final position, and controlling acceleration of the first vehicle component from a starting position to the final position according to the determined acceleration rate.
A method according to an aspect of the present invention comprises the steps of determining an accepted force on the second vehicle component, which force during operation results from an acceleration movement of the first vehicle component, determining a magnitude of an acceleration rate of the first vehicle component such that the accepted force on the second vehicle component is not exceeded and controlling acceleration of the first vehicle component according to the determined acceleration rate. The term “acceleration” here has the meaning of either a positive acceleration, i.e. speed increase or a negative acceleration, i.e. speed decrease. In other words, a negative acceleration is a deceleration or retardation.
According to one embodiment, the determined accepted force on the second vehicle component from said acceleration movement is substantially the same regardless of the magnitude of any load exerted on the first vehicle component and the magnitude of any relative speed of the first vehicle component before initiation of the acceleration.
Further preferred embodiments and advantages will be apparent from the following description and drawings.